Caring for the Roland Juno-106

Sep 18, 2016

Roland’s Juno-106 is one of the most popular polysynths ever made. It is simple to use, it sounds warm and lush and along with it’s signature chorused pad sounds it is a versatile bass synth with it’s single oscillator per voice, it’s DCO architecture keeps it in tune and you would have to work really hard to make it sound bad. It’s an instant gratification machine that has been an ever present part of modern electronic music. Many 106’s have now passed their 30th birthday and are still going strong, but what about the future of these instruments? Is it possible to keep them going for another thirty years? Here are some ways to do so, and a timely warning.

Happily, for the army of Juno-106 users out there the answer is yes, the 106 can indeed be maintained well into the future. The Juno-106 was designed and built very well by Roland and they have few reliability issues if looked after carefully. The most common components that can cause problems are the infamous 80017A “voice” modules that contain the VCF and VCA for each voice. Other less common issues are noisy chorus circuits and erratic sliders, pots and switches due to dirt or lack of regular use. There are now some other issues appearing and they are more serious but very easily fixed and in this post I want to bring these to the attention of all Juno-106 owners because a little bit bit of simple preventative maintenance is now important.

Juno-106 and an upgraded Kiwi-106 version

The Juno-106 S has built in speakers

Because of the popularity of the Juno-106 and the large number in circulation some enterprising people have gone to the effort to design replacement parts and upgrades for the Juno which will make this synth a viable machine for many, many years into the future. This is great news for Juno owners and players. Thanks to businesses such as Syntaur, Analogue Renaissance, Synthgraphics and New Zealand’s KiwiTechnics the Juno-106 has a bright future. If you are lucky enough to own one of these instruments you are holding an integral part of the history of electronic music and your stewardship of your instrument is a part of that history.

First, the easy stuff…

The output jacks and gain switch

Many issues that bring vintage synths into the tech shop are avoidable. One of the biggest ones is controls that don’t work correctly, not because they are worn out or broken but because they are dirty or more commonly suffering from lack of use. Take the little slide switch on the back of the 106 beside the output jacks for example. On many machines it may get set to one position a left that way for decades. The same goes for pots and jacks. Some just never get used. Jacks that have a switch contact inside can tarnish and in many mono synths this can cause pitch problems if the dirty switch happens to be the one inside the CV input socket.

It is good practice to go around all of your gear periodically and exercise every pot, switch, key and control and to insert and remove a jack several times into every socket to prevent build up of tarnish on the contact surfaces. If you have a Juno of any type, next time you use it grab that little switch and operate it back and forth 10 or so times. This switch is notorious for making the audio cut in and out when dirty. And of course it’s important to keep the dust out of those sliders – put a cover over your Juno when you aren’t using it for a period and if storing it away.

Spare parts and repairs

An original 80017A opened (top) and some modern clones

Many of the components inside a Juno-106 are standard parts that are still in production. For the more esoteric parts, Syntaur sells newly manufactured components – sliders and slider caps, knobs and pots, switches, pitch bend wheels and more as well as a range of second hand parts. The 80017A “voice chips” have been cloned and vastly improved by Analogue Renaissance who have also re-created the wave generator modules which fail much less frequently. The top panel buttons are standard tactile switches and for the most part the other components are still easy to find as NOS items on Ebay.

Unless you have serious physical damage to your Juno it is unlikely to ever be unrepairable. The only thing that is liable to cause considerable damage to the 106 is an over-voltage failure in the power supply and I will address this later in the post. In the image to the left you can see an original 80017A module at the top which has had it’s black coating removed to expose the circuitry. Below it are two versions of a modern equivalent module. These new versions sound identical and have none of the problems of the original part.

The Panasonic MN3009 bucket brigade delay chip

One of the problem areas of the 106 that has not yet been solved is the noise issue that can develop within the chorus circuit. While the chorus has always been a little noisy the bucket brigade IC’s that produce the time delay that creates the stereo chorus effect can sometimes become worse over time and the result is a rising and falling whooshing sound that is noticeable when they chorus is turned on and the keys are not being played.

The IC’s in question are Panasonic MN3009 256 stage bucket brigade chips. They are long out of manufacture and while there are many offered on Ebay out of China I suspect that many may not be genuine so beware if you are buying them to source them from a reputable dealer. If your chorus is excessively noisy replacing one or both of the MN3009’s will almost certainly cure the problem. They are located on the jack board on the left hand underside of the top panel. I think that it is only a matter of time before someone designs a replacement assembly for these chips using a currently available part as demand for a replacement increases.

Update Dec 2019: As hoped the MN3009 IC has been reproduced this year and is available at a reasonable cost, this is great news for those who own the various Roland synths and pedals that use this delay IC.

The jack board showing the chorus circuit

The mains transformer – Do not touch!

If you are ever tempted to work on your 106 yourself rather than taking it to a qualified tech workshop please be certain that you never open the case while the power is connected. As you can see from the photo of the mains transformer above there is exposed high tension wiring on the right hand side of the synth when it’s open.

Upgrades

The Kiwi-106 replacement CPU board

Kiwi-106 between the module and power supply boards

The Kiwi-106 also replaces the slave CPU

Synthgraphics Kiwi-106 panel overlay

Another exciting development for the Juno-106 is from New Zealand’s KiwiTechnics. Already well known for their Roland JX-3P and Korg Polysix upgrades they also produce a replacement CPU board for the Juno-106 that increases the power and editing capability of the 106 by an order of magnitude without interfering with the original sound of the synth. The Kiwi-106 adds almost 2 dozen new features to the Juno-106, brings it’s MIDI into the 21st century, adds an extra envelope generator, multiple LFO’s with many new wave shapes, internal sequencers and arpeggiators, powerful clocking options, more patches that are stored in flash, new key modes and a chord mode to name a few. It even has an editor/librarian application available for your computer.

What’s particularly relevant to this discussion about the Kiwi-106 is that by installing the upgrade you immediately improve the reliability and lifespan of the Juno because it replaces the entire CPU board and also the slave CPU on the module board thereby eliminating many old parts and of course the battery. Installation takes some careful desoldering but once it’s in it is easy to remove the Kiwi board and re-install the original parts if you want to return the Juno to it’s original state.

As you can see in some of the photos there is a high quality overlay available for the top panel from a business called Synthgraphics that shows the layout of the new control menus that the Kiwi-106 provides. This was especially good for the Juno featured in this blog post as it had a somewhat rough top panel with some surface rust and damaged paint so it made a perfect candidate for the upgrade.

Finally, a gentle warning.

The 106’s power supply heat sink

A transistor on the 106’s heat sink

The Juno-106, like all other synthesizers has transistors and voltage regulators in their power supply that run quite hot as they supply current to the synth circuits. Manufacturers usually bolted those components to a metal heat sink inside the machine such as can be seen in the above photos of the 106’s power supply. The same system can be found in the other Junos, the Jupiter 6 and many other synths. An alternative was to bolt them onto the metal rear panel of the synth to allow the case of the instrument to carry the heat away. This is the reason that machines can have hot spots on the case. Some machines such as the Prophet 5 and the Jupiter 8 have external finned heat sinks mounted outside which you can see in pictures of these machines. The problem is that as these components heat and cool over and over through the years the thermal expansion can eventually crack the solder that connects their leads to the circuit board.

Circular cracks on power supply solder joints

The image above shows the underside of the power supply board and the legs of one the transistors. This transistor drops the 22V from the rectifier diodes down to the 15V required by the synth circuitry. It does this under the control of a voltage regulator IC. The third device on the heat sink is a regulator that drops the roughly 12V supply down to the exact 5V that the digital circuits in the Juno require. Each time the synth is turned on or off these parts heat and cool down and eventually the metal expansion and contraction cracks the solder joints around the legs. At best this can cause erratic operation of the synth as the poor contact of the fractured joints glitch the computer. At worst it’s possible for a joint to go open circuit and cause an over voltage situation to occur and damage the synth.

In the image you can see the fracture rings on the centre and RHS legs, I forced the leg on the left down a little to better show what is going on. I remove the power supply board on every Juno that I service now and re-solder all 9 pins without exception. I find one or more pins have hairline cracks on more than a third of the Juno’s that I service. It is a quick and simple job to fix this issue and it is important preventative maintenance. I would advocate that service techs check the legs on any devices mounted to a heat sink on any vintage synth now as a standard part of servicing synths of this age. No doubt many techs already do this.

Above is a photo of two of the three voltage regulators in the Juno-106 power supply. The one on the left is a dual regulator, an M5230L and it handles the power supply rails for the analog circuitry. While not urgent I would also consider replacing this device in years to come as it’s failure mode seems to be over-voltage.

I recommend that when any Juno-106 goes in for service or for a battery or voice chip replacement or for any other issue or upgrade that you ask your tech as a part of the service that the solder joints on the heat sink mounted devices be refreshed. It’s a simple job that will extend the lifespan of the synth. it’s not something to panic about, no need for a trip to the synth doc just for this, it’s just a good idea to add it to the to-do list next time your Juno needs to be serviced.

Juno-106 buying guide and common issues

The Juno-106 was a big success for Roland and there were many manufactured and sold. There are still considerable numbers of them in active service and now that they are recognised as a classic their prices have risen. If you are in the market for one it’s worth holding out for a nice example. If you find one that you like it doesn’t take long to test every slider and button, look for buttons that need to be pressed hard to operate, listen for crackly sliders and particularly a crackly volume pot, test every key and of course listen for missing or incorrect sounding voices. If you have the time let it warm up for 20 minutes or so as marginal voice chips tend to get worse as they get hotter. Don’t forget to check that the MIDI in and out are working and that the bend wheel modulation works when you push the wheel forward. (Push the little LFO slider up first). Switch the chorus buttons on and off and check that the chorus is working and not too noisy (There will always be a little noise though). Enjoy your new Juno!